This replaces the `sync.Pool` allocator with lib/pool. This
implements a pool of buffers of up to 64MB which can be re-used but is
flushed every 5 seconds.
If `--use-mmap` is set then rclone will use mmap for memory
allocations which is much better at returning memory to the OS.
Before this change any attempt to access a google doc in an rclone
mount would give the error "partial downloads are not supported while
exporting Google Documents" as the mount uses ranged requests to read
data.
This implements ranged requests for a limited number of scenarios,
just enough so that Google docs can be cat-ed from an rclone mount.
When they are cat-ed then they receive their correct size also.
Before this change the union remote was using whether the writable
union could poll for changes to decide whether the union mount could
poll for changes.
The fix causes the union backend to signal it can poll for changes if
**any** of the remotes can poll for changes.
Before this change it was setting the modification times of the things
that the symlinks pointed to.
Note that this is only implemented for unix style OSes. Other OSes
will not attempt to set the modification time of a symlink.
Previously to this change, backends without the optional interface
DirMove could not rename directories.
This change uses the new operations.DirMove call to implement renaming
directories which will fall back to Move/Copy as necessary.
This will mean rclone tracks the minimum sleep values more precisely
when it isn't rate limiting.
Allowing burst is good for some backends (eg Google Drive).
If the upload concurrency is set > 1 then the hash becomes corrupted.
The upload is fine, and can be downloaded fine, however the hash is no
longer the md5sum of the object. It is not known whether this is
rclone's fault or a bug at QingStor.
